Sperry Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sperry Observatory clear sky chart from 2005-11-06 to 2024-11-04.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	17% 6% 2 6% 4 4 4 4 5% 7% 39%	101319
	Night	18% 7% 2 6% 4 4 4 3 5% 6% 42%	97694
Transparency	Day	41% 6% 12% 22% 16% 2	104864
	Night	41% 6% 12% 23% 16% 2	102238
Seeing	Day	20% 14% 30% 22% 11% 3	14997
	Night	20% 12% 32% 27% 9% 1	24153

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	15% 7% 2 5% 4 4 3 3 5% 4 48%	2517
	11th to 20th	Day	16% 10% 3 6% 5% 4 5% 4 5% 6% 37%	2520
	21st to end	Day	22% 12% 5% 7% 4 3 3 2 4 5% 33%	3042
February	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 39%	1710
	11th to 20th	Day	15% 8% 2 7% 5% 4 4 3 4 6% 44%	1845
	21st to end	Day	20% 8% 2 6% 4 4 4 4 5% 6% 37%	1570
March	1st to 10th	Day	27% 8% 2 5% 4 3 3 3 4 5% 36%	3116
	11th to 20th	Day	10% 5% 2 5% 6% 5% 4 4 6% 7% 45%	3370
	21st to end	Day	21% 6% 2 6% 3 3 3 3 4 6% 43%	4120
April	1st to 10th	Day	18% 8% 3 5% 4 4 5% 4 5% 6% 38%	2280
	11th to 20th	Day	18% 6% 2 6% 4 4 4 4 5% 8% 41%	2254
	21st to end	Day	20% 6% 2 5% 4 4 4 4 5% 6% 40%	2282
May	1st to 10th	Day	29% 8% 2 5% 4 4 3 3 5% 7% 30%	4106
	11th to 20th	Day	25% 7% 3 7% 4 4 4 3 5% 7% 31%	4389
	21st to end	Day	14% 5% 2 5% 4 4 4 3 5% 9% 44%	4837
June	1st to 10th	Day	16% 5% 2 5% 4 5% 6% 4 7% 9% 37%	2660
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	2660
	21st to end	Day	12% 5% 2 6% 5% 4 5% 5% 6% 9% 40%	2660
July	1st to 10th	Day	9% 6% 2 7% 5% 6% 6% 5% 8% 10% 35%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 6% 7% 10% 38%	4440
	21st to end	Day	14% 8% 3 8% 5% 6% 6% 5% 7% 8% 31%	4814
August	1st to 10th	Day	21% 5% 2 6% 5% 4 5% 4 6% 9% 32%	4145
	11th to 20th	Day	14% 5% 2 6% 4 4 5% 4 5% 8% 44%	3730
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 8% 46%	4180
September	1st to 10th	Day	14% 5% 2 6% 4 4 5% 4 4 7% 44%	2280
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 5% 8% 49%	2209
	21st to end	Day	20% 5% 2 7% 4 3 4 4 4 6% 40%	2090
October	1st to 10th	Day	20% 6% 2 5% 3 3 4 4 5% 7% 41%	1967
	11th to 20th	Day	15% 5% 2 5% 4 3 4 4 4 7% 48%	1900
	21st to end	Day	20% 5% 2 4 3 4 4 3 4 6% 44%	1957
November	1st to 10th	Day	15% 6% 2 5% 3 4 3 2 4 5% 52%	1698
	11th to 20th	Day	19% 4 2 4 3 3 4 3 5% 5% 48%	1710
	21st to end	Day	16% 6% 2 4 3 4 4 4 5% 7% 44%	1623
December	1st to 10th	Day	19% 8% 2 6% 4 3 3 3 6% 7% 39%	1520
	11th to 20th	Day	21% 6% 2 3 3 2 4 3 4 6% 44%	1906
	21st to end	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	2772
January	1st to 10th	Night	16% 7% 2 5% 3 3 4 3 5% 6% 47%	4429
	11th to 20th	Night	17% 9% 3 6% 4 4 4 3 4 5% 43%	4440
	21st to end	Night	24% 11% 3 5% 4 3 3 3 4 5% 35%	4596
February	1st to 10th	Night	16% 9% 3 5% 4 4 3 4 4 5% 42%	2470
	11th to 20th	Night	17% 9% 3 6% 5% 3 3 3 5% 5% 42%	2219
	21st to end	Night	20% 8% 2 5% 3 4 4 3 4 5% 43%	1884
March	1st to 10th	Night	23% 10% 3 6% 4 4 3 3 3 5% 37%	3724
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 4 6% 48%	3585
	21st to end	Night	20% 8% 3 5% 3 3 3 3 4 4 43%	3511
April	1st to 10th	Night	20% 7% 2 5% 4 4 5% 3 5% 7% 38%	1900
	11th to 20th	Night	17% 8% 2 6% 4 4 4 3 5% 8% 40%	1875
	21st to end	Night	19% 6% 2 5% 4 3 4 4 4 6% 42%	1895
May	1st to 10th	Night	26% 9% 3 7% 4 3 3 3 4 6% 30%	2834
	11th to 20th	Night	26% 8% 3 7% 5% 3 3 3 4 6% 33%	2532
	21st to end	Night	17% 7% 2 6% 3 3 4 3 5% 9% 41%	2738
June	1st to 10th	Night	16% 6% 2 5% 4 4 4 5% 6% 8% 40%	1520
	11th to 20th	Night	14% 6% 2 4 4 5% 4 4 6% 9% 41%	1520
	21st to end	Night	11% 5% 2 5% 4 5% 5% 4 6% 10% 43%	1520
July	1st to 10th	Night	10% 6% 2 7% 5% 6% 5% 4 7% 9% 39%	2520
	11th to 20th	Night	14% 6% 2 6% 4 5% 5% 4 8% 9% 37%	2520
	21st to end	Night	17% 7% 2 6% 4 4 5% 5% 6% 8% 35%	2739
August	1st to 10th	Night	23% 6% 3 6% 5% 4 4 4 6% 8% 32%	2750
	11th to 20th	Night	14% 7% 2 7% 4 5% 5% 4 5% 7% 40%	3097
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 8% 52%	3476
September	1st to 10th	Night	15% 6% 2 6% 4 4 4 4 4 6% 44%	1900
	11th to 20th	Night	14% 5% 1 4 3 3 3 3 4 7% 52%	1970
	21st to end	Night	19% 7% 2 5% 4 4 3 3 4 5% 44%	2090
October	1st to 10th	Night	18% 7% 2 5% 4 4 3 3 5% 6% 42%	2209
	11th to 20th	Night	15% 5% 2 5% 3 3 4 2 4 6% 51%	2280
	21st to end	Night	20% 7% 2 5% 3 2 3 3 4 5% 45%	2641
November	1st to 10th	Night	13% 5% 2 6% 4 3 4 3 4 5% 52%	2453
	11th to 20th	Night	19% 6% 2 5% 3 3 3 3 4 5% 48%	2470
	21st to end	Night	15% 6% 2 5% 4 3 4 3 5% 7% 46%	2555
December	1st to 10th	Night	19% 8% 3 5% 4 3 5% 3 5% 6% 40%	2660
	11th to 20th	Night	20% 6% 2 5% 3 4 4 3 5% 6% 43%	3288
	21st to end	Night	20% 9% 3 6% 4 4 4 3 4 5% 37%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	38% 5% 12% 28% 13% 3	2518
	11th to 20th	Day	46% 7% 12% 20% 14% 2	2520
	21st to end	Day	54% 4 10% 20% 10% 2	3042
February	1st to 10th	Day	45% 5% 13% 22% 12% 2	1710
	11th to 20th	Day	43% 4 9% 24% 17% 3	1854
	21st to end	Day	47% 5% 10% 21% 14% 3	1570
March	1st to 10th	Day	49% 5% 11% 23% 9% 2	3119
	11th to 20th	Day	33% 8% 13% 29% 15% 2	3370
	21st to end	Day	43% 4 8% 16% 23% 5%	4120
April	1st to 10th	Day	44% 6% 10% 19% 16% 4	2280
	11th to 20th	Day	41% 6% 11% 21% 17% 4	2254
	21st to end	Day	43% 6% 10% 20% 18% 4	2282
May	1st to 10th	Day	54% 6% 12% 15% 12% 1	4120
	11th to 20th	Day	51% 8% 13% 17% 9% 1	4393
	21st to end	Day	35% 8% 12% 25% 18% 2	4837
June	1st to 10th	Day	41% 8% 13% 21% 15% 1	2660
	11th to 20th	Day	43% 8% 12% 23% 11% 3	2660
	21st to end	Day	39% 9% 14% 22% 16% 1	2660
July	1st to 10th	Day	42% 10% 13% 21% 14% 1	4370
	11th to 20th	Day	38% 9% 17% 21% 14% 1	4365
	21st to end	Day	48% 8% 11% 16% 16% 2	4661
August	1st to 10th	Day	47% 8% 13% 21% 9% 1	4131
	11th to 20th	Day	37% 7% 13% 29% 13% 1	3766
	21st to end	Day	34% 6% 11% 27% 20% 2	4180
September	1st to 10th	Day	40% 6% 11% 20% 20% 3	2280
	11th to 20th	Day	34% 4 11% 23% 24% 3	2209
	21st to end	Day	45% 6% 9% 18% 19% 3	2090
October	1st to 10th	Day	38% 6% 9% 18% 24% 6%	3266
	11th to 20th	Day	25% 4 11% 24% 30% 5%	3140
	21st to end	Day	27% 4 14% 25% 26% 4	3208
November	1st to 10th	Day	35% 4 12% 24% 22% 3	1698
	11th to 20th	Day	38% 4 10% 23% 21% 3	1710
	21st to end	Day	38% 5% 13% 29% 12% 3	1623
December	1st to 10th	Day	44% 5% 15% 20% 14% 1	1520
	11th to 20th	Day	41% 5% 16% 23% 12% 3	1906
	21st to end	Day	49% 9% 11% 23% 9%	2772
January	1st to 10th	Night	39% 5% 10% 30% 12% 3	4429
	11th to 20th	Night	44% 4 13% 24% 12% 2	4440
	21st to end	Night	51% 5% 9% 22% 12% 2	4596
February	1st to 10th	Night	44% 5% 12% 24% 12% 2	2470
	11th to 20th	Night	45% 4 9% 19% 18% 5%	2221
	21st to end	Night	43% 5% 7% 25% 17% 4	1884
March	1st to 10th	Night	50% 4 10% 22% 11% 3	3734
	11th to 20th	Night	35% 6% 14% 24% 17% 3	3586
	21st to end	Night	44% 5% 7% 15% 21% 7%	3511
April	1st to 10th	Night	46% 6% 10% 19% 16% 4	1900
	11th to 20th	Night	44% 5% 10% 19% 20% 2	1875
	21st to end	Night	42% 6% 9% 21% 18% 4	1895
May	1st to 10th	Night	54% 6% 11% 17% 10% 1	2840
	11th to 20th	Night	53% 7% 13% 14% 10% 2	2533
	21st to end	Night	39% 8% 15% 23% 13% 3	2739
June	1st to 10th	Night	40% 7% 11% 21% 19% 2	1520
	11th to 20th	Night	38% 8% 14% 25% 13% 1	1520
	21st to end	Night	35% 8% 16% 23% 16% 1	1520
July	1st to 10th	Night	40% 10% 16% 19% 13% 2	2480
	11th to 20th	Night	40% 9% 14% 23% 12% 1	2472
	21st to end	Night	44% 8% 15% 14% 17% 2	2651
August	1st to 10th	Night	50% 7% 17% 16% 9% 1	2740
	11th to 20th	Night	42% 8% 11% 27% 11% 1	3127
	21st to end	Night	31% 6% 10% 30% 21% 1	3476
September	1st to 10th	Night	40% 7% 11% 23% 19% 2	1900
	11th to 20th	Night	33% 6% 12% 22% 25% 3	1970
	21st to end	Night	43% 4 8% 22% 21% 2	2090
October	1st to 10th	Night	38% 6% 11% 23% 20% 2	3690
	11th to 20th	Night	24% 4 10% 27% 30% 4	3779
	21st to end	Night	30% 4 11% 30% 23% 2	4340
November	1st to 10th	Night	34% 5% 11% 24% 22% 4	2453
	11th to 20th	Night	39% 5% 9% 24% 18% 5%	2470
	21st to end	Night	37% 5% 14% 27% 15% 1	2555
December	1st to 10th	Night	45% 5% 12% 23% 13% 2	2660
	11th to 20th	Night	42% 5% 13% 21% 16% 3	3288
	21st to end	Night	48% 7% 12% 21% 12% 1	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	18% 31% 31% 17% 4 1	180
	11th to 20th	Day	24% 34% 30% 10% 2	180
	21st to end	Day	23% 22% 37% 12% 4 1	276
February	1st to 10th	Day	27% 24% 35% 11% 3	270
	11th to 20th	Day	24% 21% 40% 13% 2	453
	21st to end	Day	27% 21% 33% 15% 4	382
March	1st to 10th	Day	22% 25% 32% 18% 4	460
	11th to 20th	Day	22% 23% 34% 15% 4 1	460
	21st to end	Day	26% 21% 33% 14% 4 1	506
April	1st to 10th	Day	26% 21% 33% 14% 6% 1	460
	11th to 20th	Day	23% 22% 30% 15% 9% 2	452
	21st to end	Day	29% 17% 31% 18% 3 2	460
May	1st to 10th	Day	30% 19% 27% 16% 6% 2	463
	11th to 20th	Day	23% 13% 33% 22% 8% 1	487
	21st to end	Day	19% 7% 28% 28% 15% 3	529
June	1st to 10th	Day	17% 11% 31% 25% 14% 2	490
	11th to 20th	Day	15% 11% 33% 27% 12% 2	490
	21st to end	Day	16% 8% 32% 27% 14% 2	490
July	1st to 10th	Day	12% 6% 24% 34% 18% 7%	485
	11th to 20th	Day	10% 3 26% 33% 23% 5%	484
	21st to end	Day	15% 6% 28% 32% 16% 3	532
August	1st to 10th	Day	12% 7% 23% 33% 19% 6%	486
	11th to 20th	Day	14% 5% 22% 35% 18% 6%	479
	21st to end	Day	14% 7% 26% 30% 16% 7%	539
September	1st to 10th	Day	18% 9% 25% 26% 17% 7%	490
	11th to 20th	Day	15% 7% 26% 26% 16% 10%	490
	21st to end	Day	23% 11% 28% 23% 11% 4	490
October	1st to 10th	Day	24% 8% 28% 22% 13% 5%	490
	11th to 20th	Day	16% 16% 29% 26% 11% 2	490
	21st to end	Day	24% 12% 33% 20% 9% 2	469
November	1st to 10th	Day	16% 14% 31% 24% 11% 3	374
	11th to 20th	Day	23% 19% 30% 21% 6%	370
	21st to end	Day	18% 17% 36% 22% 6% 1	283
December	1st to 10th	Day	22% 29% 29% 13% 6% 1	180
	11th to 20th	Day	29% 24% 29% 14% 4	180
	21st to end	Day	25% 19% 35% 16% 5% 1	198
January	1st to 10th	Night	19% 19% 39% 20% 3	760
	11th to 20th	Night	24% 17% 33% 23% 3	760
	21st to end	Night	18% 18% 42% 19% 2	836
February	1st to 10th	Night	21% 15% 39% 23% 1	760
	11th to 20th	Night	22% 21% 39% 17% 1	743
	21st to end	Night	24% 19% 36% 19% 3	628
March	1st to 10th	Night	22% 18% 36% 21% 4	760
	11th to 20th	Night	22% 16% 38% 20% 3 1	760
	21st to end	Night	21% 15% 40% 19% 5%	836
April	1st to 10th	Night	22% 18% 35% 20% 4	760
	11th to 20th	Night	21% 13% 37% 23% 5%	751
	21st to end	Night	22% 12% 35% 25% 5% 1	755
May	1st to 10th	Night	25% 12% 34% 21% 7%	570
	11th to 20th	Night	23% 9% 35% 25% 8%	398
	21st to end	Night	19% 5% 23% 39% 13% 1	411
June	1st to 10th	Night	18% 6% 28% 35% 12%	380
	11th to 20th	Night	14% 5% 28% 39% 14%	380
	21st to end	Night	10% 4 28% 47% 11%	380
July	1st to 10th	Night	12% 5% 23% 39% 20% 2	370
	11th to 20th	Night	13% 4 20% 43% 19% 1	368
	21st to end	Night	13% 3 24% 45% 14% 1	416
August	1st to 10th	Night	13% 3 18% 44% 21% 2	518
	11th to 20th	Night	15% 4 18% 37% 25% 1	750
	21st to end	Night	16% 3 19% 39% 21% 2	836
September	1st to 10th	Night	15% 4 27% 34% 18% 2	760
	11th to 20th	Night	17% 4 22% 33% 20% 4	760
	21st to end	Night	21% 6% 26% 32% 14% 1	760
October	1st to 10th	Night	22% 7% 29% 25% 15% 2	760
	11th to 20th	Night	18% 10% 30% 31% 11%	760
	21st to end	Night	23% 9% 34% 24% 9%	836
November	1st to 10th	Night	15% 11% 34% 27% 12% 1	755
	11th to 20th	Night	22% 14% 32% 24% 7%	760
	21st to end	Night	17% 16% 35% 24% 6% 1	760
December	1st to 10th	Night	24% 16% 33% 22% 5% 1	760
	11th to 20th	Night	22% 15% 37% 22% 4	760
	21st to end	Night	23% 14% 37% 24% 2	836

Page generated at 2024-11-01 22:47:47. Version ac07

Copyright © 2024 Attilla Danko.